This application claims the priority of Japanese Patent Application No. 6-67626 filed on Mar. 9, 1994.
1. Field of the Invention
The present invention relates to a field sequential image pickup apparatus and, more particularly, to the structure of a circuit which is used for a field sequential electronic endoscope apparatus or the like so as to process an image while taking a movement in an object of observation into consideration.
2. Description of the Related Art
As an image pickup apparatus, there is an electronic endoscope for observing a body cavity such as an alimentary canal by using a CCD (Charge Coupled Device) as a solid-state image pickup device. In some of such field sequential apparatuses, not only a visible image is formed by R (red), G (green) and B (blue) light but also an infrared image is formed by infrared light (e.g. near infrared light). According to these apparatuses, it is possible to simultaneously observe an ordinary color picture and a cortical portion or submucous blood flow in a body cavity with infrared light. When an image of the object of observation is displayed on a monitor, it is also possible to display a freeze (still) image by operating a freeze button or the like. That is, a desired still image is displayed on a monitor by pressing a freeze button in accordance with a freeze command issued under the control of the reading operation of the picture signals sequentially stored in a memory. Owing to such a freeze image, detailed observation of an object is enabled, and it is possible to record the freeze image in the form of a photograph and a video image.
Such a sequential image pickup apparatus, however, suffers from a problem that when there is a movement in an object of observation, there is misregistration in color images. In a visible image, RGB light beams are sequentially projected through a color (filter) disks so as to form RGB picture signals, and these RGB picture signals are mixed and simultaneously processed. Therefore, when there is a movement of an object of observation, a positional difference is caused among RGB signals, which are obtained in time series, in correspondence with a difference in the moving speed, which results in misregistration in color images. To prevent this, in a conventional apparatus, a movement at an object of observation is detected so as to inhibit a freezing operation when there is a movement, while executing a freezing operation when there is no movement.
In an infrared image, however, a monochromatic image is displayed, so that there is no problem in misregistration in color images. In other words, there is no necessity of controlling a freezing operation in accordance with the movement of an object of observation. On the contrary, it is expected to display and record a freeze image, at the point of time which is the optimum for observation without missing a shutter chance when there is a movement in an object of observation. In contrast, where there is no movement, it is necessary to display as clear an image as possible with an improved S/N.